Inhibitor



252. UUMPUSI IIUNS,

UNITED STATES aminer PATENT OFFICE INHIBITOR No Drawing.

Application November 28, 1936,

Serial No. 113,264 6 Claims. (oLfls-s) This invention relates to the inhibition of the action of acids on metals, and is particularly directed to processes wherein cinchona bark alkaloids are sulfurized in the presence of concentrated sulfuric acid, to the novel sulfurized sulfation products of cinchona bark alkaloids produced, and to the use of these novel products for inhibiting the action of acids on metals.

Pickling and metal cleaning operations frequently involve the use of a bath of dilute nonoxidizing acids such as sulfuric, hydrochloric, acetic, formic, aqueous solutions of acid sulfates, and the like. Such baths are used for numerous purposes, a typical example of which is the pickling of iron or steel articles such as wire, sheet, and other manufactures. The composition, concentration, temperature of operation, and other factors vary with different baths, but in every instance the primary function of a bath is the removal of undesirable incrustations. As soon as the base metal becomes exposed, it is, in the absence of an inhibitor, attacked by the bath with consequent damage to the article and with an unnecessary consumption of acid.

The application of my invention to acid pickling and acid metal cleaning operations involves no change in the customary baths and processes, except for the addition of a small amount of an inhibitor of this invention. In quantities as small as about one hundredth of one per cent, my novel inhibitors will check the attack of acid upon metal. I usually prefer to employ between two hundredths of one per cent and one tenth of one per cent of one of my inhibitors, but more or less may be used if desired.

While the inhibitors of this application are primarily adapted for use in metal cleaning and pickling processes, they may, of course, be used in numerous other relations as are the inhibitors already known to the art.

Many commercial inhibitors known to have high inhibiting efiiciency possess the disadvantage of being diflicultly soluble in dilute acids. They dissolve slowly when added to pickling baths. Particles of inhibitor which have not had sufficient time to dissolve float on the surface of the acid. Such particles are frequently picked up by work removed from the bath, entailing inhibitor loss and causing pickled work to be dirty. Because the amoimt of inhibitor lost in this manner varies, the action of the pickling bath is diflicult to control accurately.

Moreover, many inhibitors contain residues which do not dissolve in the pickling acid even after a prolonged period. Such undissolved residues, in finely divided form, often adhere to pickled work and cause it to appear stained.

I have found that an inhibitor without these disadvantages may be produced by sulfurizing a cinchona bark alkaloid in the presence of concentrated sulfuric acid.

The cinchona bark alkaloids, sometimes termed quinine alkaloids, are very complicated in their chemical character, and their exact molecular configuration is not well understood. It is generally believed that the compounds making up the cinchona bark alkaloids are characterized by the presence of two ternary nitrogen atoms, one of which is bonded to two carbon atoms, and the other of which is bonded to three different carbon atoms. Typical of the cinchona bark alkaloids are quinine, quinidine, cinchronine, and quinoidine. Quinoidine, the by-product of the extraction of medicinal alkaloids from cinchona bark, is a particularly satisfactory material for use in making my novel inhibitors.

A cinchona bark alkaloid sulfated and sulfurized in the manner of my invention is completely soluble in dilute non-oxidizing acids. It dissolves rapidly and leaves no objectionable residue to contaminate pickled work.

A further advantage of the inhibitors of my invention is that they sink immediately to the bottom when added to a pickling bath. Hence work being pickled comes into contact only with inhibited solution, instead of with acid containing undissolved inhibitor. This results in a saving of inhibitor and in the production of cleaner pickled work. Furthermore, the exact amount of.

dissolved inhibitor in a pickling tank can be calculated, making possible more accurate control of pickling operations and greater acid economy.

ro cts of ciny suln the presence of concentrated sulfuric acid. The sulfurization may be accomplished by methods already known for sulfurizing cinchona bark alkaloids, such as heating with elemental sulfur, or treating with suliuryl chloride with or without a catalyst present.

It seems likely, from their mode of preparation, that the novel compositions of my invention are actually sulfation products containing the R-O-SOaH group, but it may be that a part or all of the products are sulfonated, rather than sulfated. I shall accordingly use the term sulfation in a generic sense, as is customary in the art, to include true sulfation or sulfonation or both.

I do not clearly understand the nature of the reactions invloved in sulfurizing cinchona bark alkaloids in the presence of sulfuric acid, but the evidence available to me indicates that the sulfuric acid is chemically combined with the alkaloids. The flnal product when dispersed in water gives a solution which is only slightly acidic, and the amount of sulfuric acid which is used is much greater than theoretically could be combined with the nitrogen in the cinchona bark alkaloids if the sulfuric acid is assumed to add on at the nitrogen atoms. Furthermore, treatment of sulfurized cinchona bark alkaloids with sulfuric acid subsequent to sulfurization does not give a completely soluble product, indicating that the sulfurization is in some manner directed or controlled by the presence of the acid.

The nature of my novel inhibitor and the processes of its manufacture and use may be more clearly understood from the following examples:

Example I 50% H2804 solution 21. Qninnirline 30. Sulfur 3.87

These ingredients were mixed with a mechanical agitator for 15 minutes at about 30 C. The temperature was then raised to C. over a period of 20 minutes by heating the oil-bath, held at 130 C. for 15 minutes, raised to C. over a period of 45 minutes and held at 170 C. for 45 minutes. A considerable volume of gas, chiefly hydrogen sulfide and water vapor, was evolved during heating. The product was cooled, removed from the kettle, and ground to a powder.

A solubility test was made by adding 1.2 grams of this powdered sulfurized sulfation product of quinoidine to 1000 grams of 5% sulfuric acid solulution at F. The powder sank immediately to the bottom of the solution and dissolved rapidly and completely. A solution containing 0.12% inhibitor was thus obtained.

The efliciency of this inhibitor was tested as follows:

Two 2" x 3" x 26 gage pieces of low-carbon hot-rolled steel sheet were freed of scale, carefully cleaned, and weighed. They were then submerged for 20 minutes in 500 grams of 5% sulfuric acid solution in which had been dissolved 0.0057% of the sulfurized sulfation product of quinoidine prepared in Example I. The solution was maintained at 180 F. during the test. At the end of the 20 minute period the strips were removed, washed, dried, and reweighed. The same test was made on fresh test strips in a solution containing no inhibitor. The loss in weight of the strips in the inhibited acid was found to be only 22.6% of the loss of the strips in uninhibited acid.

A sulfurized cinchona bark alkaloid which is essentially different from the product of Example I is obtained if the sulfuric acid solution is not present during the sulfurization. This was evidenced by sulfurizing quinoidine, following the procedure of Example I except omitting the sulfuric acid. A solubility test was made by adding 1.2 grams of this sulfurized quinoidine to 1000 grams of 5% sulfuric acid solution at 180 F. The sulfurized quinoidine floated on the surface of the solution and dissolved slowly. There remained a considerable insoluble residue. Further tests were made, reducing the amount of inhibitor added, but even when the amount was only 0.05 gram there remained a noticeable undissolved residue.

An efiiciency test was made following the method of Example I. A concentration of 0.0050% of sulfurized quinoidine was used giving a comparison with the product of Example I on an equivalent quinoidine basis. In this instance, the loss in weight of the strips in inhibited acid was found to be 25.4% of the loss of the strips in uninhibited acid.

The product obtained by treatment of a sulfurized cinchona bark alkaloid with sulfuric acid subsequent to sulfurization is, moreover, not the same as the product obtained when the acid is present during sulfurization. This was shown by sulfurizing 30.0 parts by weight of quinoidine with 3.87 parts of sulfur, following the procedure of Example I but omitting the sulfuric acid solution. when sulfurization was complete, 21.0 parts of 50% sulfuric acid was added and the batch heated for an additional 45 minutes. It was then cooled. The product was a sticky, pasty mass which could not be readily ground to a powder. Solubility tests were made as in Example I. The product tended to float on the surface and dissolved slowly. There remained a noticeable undissolved residue.

Commercial 60 B. acid, containing about 77.8% H3304 by weight, may be used instead of the 50% solution of Example I, as is demonstrated by the following example:

Example II A batch was made by the process of Example I. The proportions of materials used are indicated as parts by weight.

Sulfuric acid 77.8% solution (60 B.) 20.2 Quinoidine 45.0 Sulfur 5.8

The reaction product was completely and readily soluble in 5% sulfuric acid at 180 F.

The above examples are only illustrative of my invention and it will be readily apparent to one skilled in the art that considerable variation of the conditions is possible.

The proportion of sulfuric acid to cinchona bark alkaloid may be widely varied, tho generally I prefer to use from about 15 to 45% H2804 based on the weight of cinchona bark alkaloid. More specifically, I prefer to use about 35%. The initial concentration of sulfuric acid is relatively unimportant since, if dilute acid is used, water will be evaporated during the reaction. Ultimately, therefore, a concentrated acid is in any event obtained. I have used acid solutions having initial concentrations of from about 35 to 93% H2804, but I prefer to use a solution containing about 78% H2804, which is the 60 B. acid known to commerce.

The amount of sulfur used may also be widely varied according to the usual practice for the sulfurization of cinchona bark alkaloids. The amounts of sulfur used in the above examples represent about an optimum under the conditions shown, but the advantages of my invention may be obtained with greater or smaller examples, I have found an oil-jacketed kettle 75 suitable for the purpose. Agitation oi the reaction mixture is helpful in avoiding local overheating and facilitates contact of the mixture with the heat sources. Agitation is, of course, not essential to the process.

A wide variation of time and temperature conditions is possible in the operation of my novel processes without departing from the scope of my invention. The ultimate temperature attained must be high enough to permit the reaction to proceed properly, and not so high as to result in thermal decomposition of the product. The rate at which this ultimate temperature is reached may also be widely varied without materially altering the results obtained. I have found the time and temperature control of Exa'mples I and II satisfactory and convenient for the conditions of these examples.

I claim:

1. In a process of cleaning and pickling metal, the step comprising treating said metal with a dilute, non-oxidizing acid containing therefor: an inhibitor produced by mixing a cinchona bark alkaloid, sulfur, and sulfuric acid and heating the mixture to cause chemical interaction.

2. In a process of cleaning and pickling metal, the step comprising treating said metal with a lu-flullllllui dilute, non-oxidizing acid containing an inhibitor produced by mixing quinoidine, sulfur and sul-- furic acid and heating the mixture to cause chemical interaction.

3. A cleaning and pickling bath for metals comprising a dilute non-oxidizing acid containing a small amount of an inhibitor produced by mixing a cinchona bark alkaloid, sulfur and sulfuric acid and heating the mixture to cause chemical interaction.

4. A cleaning and pickling bath for metals comprising a dilute non-oxidizing acid containing a small amount of an inhibitor produced by mixing quinoidine, sulfur and sulfuric acid and heating the mixture to cause chemical interaction.

5. In a process of making a sulfurized sulfation product of a cinchona bark alkaloid the steps comprising mixing a cinchona bark alkaloid, sulfur and sulfuric acid and heating the mixture to cause chemical interaction.

6. An inhibitor comprising the product produced by mixing a cinchona bark alkaloid, sulfur and sulfuric acid and heating the mixture to cause chemical interaction.

FRED C. CARL-SON. 

